Hardenable epoxy resin and processes for preparing and hardening same



United States Patent 2,987,498 HARDENABLE EPOXY RESIN AND PROCESSES FORPREPARING AND HARDENING SAME Jan Ide de Jong, Blnricum, Netherlands,assignor to Koninklijke Zwavelzuurfabrieken v/h Ketjen N.V., Amsterdam,Netherlands, a limited liability company No Drawing. Filed Feb. 4, 1959,Ser. No. 791,026 Claims priority, application Netherlands Feb. 12, 1958Claims. (Cl. 260--43) It is known that the reaction of epichlorohydrinwith phenolic compounds under the influence of alkali lyes leads to theforming of condensates, containing epoxy groups The greater part of suchcondensates, which are usually called epoxy resins, is based on reactionproducts of 2-2'-diphenylolpropane and epichlorohydrin.

Such condensates are characterized by the general formula:

As a matter of fact, epoxy resins can also be prepared from otherpolyphenol bases but bisphenol. Thus epoxy resins have been obtainedfrom phenolic condensates or substituted phenols and formaldehyde. Suchcondensates are generally suitable for preparing laminates; however theyare less apt for application in the lacquer-industry. Moreover thedifierence in basic material price, compared to epoxy resins based onbisphenol A is of little importance as a rule.

The invention concerns a method for the preparation of epoxy resins,which are generally apt for application in the lacquer industry, whileat the same time the price of the basic material of these epoxy resinsis low. The new epoxy resins are obtained by reacting condensates oftechnical xylene and formaldehyde first with phenol and then withepichlorohydrin. In this way epoxy resins of greatly varying structure,composition and molecular weight can be obtained, a.o. epoxy resins canbe prepared which are apt for application in the lacquer industry.

It has appeared that the properties of the new epoxy resins depend uponthe method of preparing the precondensate, upon the choice of thephenolic component and upon the proportion of the reacting components.

Already the method for preparing the pre-condensate can be varied inseveral ways. Thus essentially also other hydrocarbons but xylene, p.e.toluene or naphthalene may be used, though as a rule xylene is preferredbecause, as is known, the xyleneformaldehyde condensates areparticularly reactive, and moreover can be easily obtained in greatquantity.

It is of importance for the method according to the invention that themolecular weight of the xylene formaldehyde condensates should besufliciently high for the medium chain length to contain more than two,preferably more than three xylene kernels, that is to say that it shouldhave a minimum molecular weight of about 2 ,987,498 Patented June 6, 1961 300. Preferably a condensate with a molecular weight of more than 400should be used. Besides, it is desirable that the oxygen content of theprecondensates should be more than about 4%, whilst preferably apre-condensate containing more than about 8-10% oxygen should be used. Ahigh oxygen content of p.e. 13-16%, which is caused by the presence ofacetal bridges etc., in which X= xylene rest) is not necessary, and isundesirable for applications which do not especially require resins witha high epoxy number. In short, preferably a pro-condensate with arelatively high molecular weight (about 500-800), a relatively lowoxygen content (about 8-l0%) and a small number of acetal groups (about0.53%) is used. The preparation of such condensates is explained in theexamples.

As the colour of the pre-condensate has an influence of the colour ofthe resulting epoxy resin, it is of importance to avoid discolouringduring the pre-condensation. This can a.o. be obtained by using as purea xylene Hi i H: H C-CH-CHr- O WO 0H C n O as possible (thus metaxylenegives colourless pre-condensates).

The second step of the process, viz. the reaction of pre-condensateswith phenols may be varied by the choice of the phenolic component andby varying the proportion by weight of the reacting components. This isknown already from the work of R. Wegler (Angew. Ch. 1948, p. 88).

Thus also paracresol, para-tert.butylphenol, bisphenol A etc., otherthan phenol, can be brought into reaction withxyleneformaldehyde-condensates.

The etherand acetal-bridges of the pre-condensates are opened thereby,so that a compound of aralkylphenols is formed while separating ofiwater. For the method according to the invention it is of essentialimportance that on an average more than one, preferably 2 phenolicgroups per molecule of such condensates, are present. For someapplications it is desirable to introduce even more than 2 phenolicgroups per molecule. By making a suitable choice of the numbers ofreacting components, it is possible, to regulate the phenolic groups,-asappears from the examples.

When phenol is chosen as a phenolic component, about 0.4-3, preferablyabout 0.1-1.2 parts of phenol per part of pre-condensate are broughtinto reaction with each other, under the influence of a very smallquantity of a strong acid catalyst, p.e. 0.01% H In this waycondensates, so called novolacquers, are obtained, which contain about20-70% phenol. The molecular weight of these novolacquers varies fromabout 300 to about 1500; preferably however, novolacquers with about35-45% phenol are used, the molecular weight of which being about500-1000.

Surprisingly it was found, that the epoxy resins, de rived from suchrelatively high molecular novolacquers, are particularly suitable forapplication in the lacquer industry, as a result of their goodflexibility and their surprisingly good adhesive properties.

As is known, the reaction of epichlorohydrin with phenols under theinfluence of alkaline catalysts can be carried out in several ways, bywhich various results can be obtained. Thus epoxy resins can be preparedwhich, apart from terminal epoxy groups, also contain secondary hydroxylgroups. It is also possible to condensate the already formed epoxyresins with novolacquers or with other phenolic compounds under theinfluence of alkaline catalysts. The way in which the condensation ofnovolacquers with epichlorohydrin is carried out, is not essential forthe invention in question. In general attempts will be made to use aslittle epichlorohydrin as possible for chainforming of the epoxy resins,in other words, from an economical point of view, eiiorts will he madeof chiefly utilizing the epichlorohydrin for the introduction ofultimate epoxy groups, the further thorough hardening of which dependsupon the epoxy resin. As a matter of fact it is. necessary for athorough hardening to introduce more than one epoxy group per molecule,preferably about 2 or more. a

From the foregoing it appears that epoxy resins with greatly varyingproperties and composition can be prepared according to the method ofthis invention, as will be illustrated in the following examples.

EXAMPLE I-A Preparation of a precondensate .ll'ZOgrams formaldehyde of35% was brought into a roundbottom flask provided with a stirrer and areflux cooler, and mixed with 638 grams sulphuric acid of 96%. Thereupon1060 grams of technical xylene were added after which the reactionmixture was heated during 5 hours while stirring and refluxing.

The oily layer was thereupon washed acid free with hot water andthereafter freed from volatile components.

Output grams-.. 1120 Molecular weight 550 Oxygen content percent 9.2vAcetal number do 1.2

EXAMPLE I-B Preparation of a novolacquer Output ams..- 1430 Novolacquer,containing 37% bound phenol o 1430 Molecular weight About 700 EXAMPLEI-C Preparation of epoxy resin 1755 grams of a novolacquer, preparedaccording to Example I-B, was dissolved in 3000 grams epichlorohydrin,after which 18 cm. water was added. After that 287 grams of solid NaOHwas added in small quantities in the course of one hour at a temperatureof 90 C. After that the reaction was completed by heating for anotherhour and the excess of epichlorohydrin was distilled 0E. The thusobtained resin was dissolved in 3 liters of benzene and filtered.

After-removing the solvent 2 kg. of a clear, slightly yellow solid resinwas obtained.

Molecular weight 7 ("a Epoxy number EXAMPLE H-A 1000. grams of apore-condensate, prepared according to- Example I-A, was brought intoreaction with 900 .xrams of phenol under the influence of 4 cm. 0.1

N H SO In this way 1530 grams of a clear brown novolacquer was obtained.

Molecular weight .....About 600 Phenol content Percent..- 41

EXAMPLE [H3 1500 grams of the novolacquer, prepared according to ExampleII-A, was dissolved in 920 grams (10 mol.) of epichlorohydrin.

The thus obtained mixture was brought into reaction with 10 cm. of waterand 265 grams (6.6 M) of NaOH at -100 C. After a reaction period of 2hours the excess of epichlorohydrin (about 300 grams) was distilled offand the epoxyresin was dissolved in 2 l. of benzene. The formed sodiumchloride was filtered OE and the solvent was distilled off.

The slightly yellow, clear, solid resin which was prepared in this wayhad an epoxynumber of 0.28 and a molecular weight of about 900.

EXAMPLE III 245 grams of a novolacquer with a molecular weight of 750and a phenol content of 38% was dissolved in 41 grams of NaOH (1 mol.)and 410 grams of water. Thereupon 140 grams of epichlorohydrin (1.5mol.) was added at 25 C.

The reaction temperature slowly rose to 55 C. which reaction temperaturewas maintained for about 2 hours. Thereupon the conversion was completedby reacting for another 2 /2 hours at C. The excess of epichlorohydrinwas distilled ofl. The resin was dissolved in 225 grams of benzene,filtered and thereafter freed from the solvent.

The thus obtained solid epoxy resin had an epoxy number of 0.16 and amolecular weight of about 1300.

EXAMPLE IV An epoxy resin, which was prepared according to Exemple III,after removal of the excess of epichlorohydrin, was washed saltfree withwater, and thereupon freed from the last traces of water by heating invacuo. The resin had an epoxy number of 0.17 and a molecular weight ofabout 1200.

EXAMPLE V 141 grams of a novolacquer was obtained by reacting 70 gramsof a pre-condensate of technical xylene and formaldehyde (M.G. 400) with93 grams of phenol.

This novolacquer, which contained 45% phenol and which had a molecularweight of about 450, was dissolved in 300 grams of epichlorohydrin. Thesemiliquid epoxy resin, which was obtained after reaction of thismixture with 28 grams of NaOH, had an epoxy number of 0.34 and a mediummolecular weight of about 600.

EXAMPLE VI 153 grams of a pro-condensate of technical xylene andformaldehyde (M.G. 500) was brought into reaction with grams oftert.butylphenol under the influence of 0.1 gram of-toluencsulfonicacid. After a reaction period of 1 hour at 150 C., 22 grams of waterwere distilled off and a clear slightly yellow novolacquer was'obtained.

This novolacquer was then brought into reaction with 368 grams ofepichlorohydrin and 33 grams of NaOH. The thus prepared clear veryslightly coloured semi-solid epoxy resin had an epoxy number of 0.20 anda molecular weight of about 650.

BXAMPLEVII 70 grams of a naphthalene-formaldehyde resin (M.G. about 500)was heated during 1% hour at C. with 70 grams of phenol and 0.1 gram ofparatoluene-sulfonic acid, after which the excess of phenol wasdistilled off. The thus prepared novolacquer (100 grams) contained 38%phenol.

After epoxydising with 300 grams of epichlorohydrin and 16 grams ofNaOH, a clear brown solid epoxy resin with an epoxy number of 0.18 and amolecular weight of about 700 was obtained.

EXAMPLE VIII 50 grams of the epoxy resin, prepared according to ExamplelI-B, was dissolved in 25 grams of toluene and 25 grams ofmethylethylketone.

This solution was mixed with 4 grams of diethylenetriamine, dissolved in3 grams of toluene and 3 grams of n.butanol.

The potlife of this solution at room temperature was about 24 hours. Thethorough hardened films of this resin were hard, clear, flexible andshowed an excellent adhesion on metals and glass.

What I claim is:

1. An epoxy resin which is the condensation product of epichlorohydrinand a substance which contains at least 2 aromatic nuclei per moleculeand which is the reaction product of a mono-nuclear phenol and an oxygencontaining condensation product of an aromatic hydrocarbon and acompound selected from the class consisting of formaldehyde andparaformaldchyde, and which oxygen containing condensation product isfree of unreacted phenol, formaldehyde and paraiormaldehyde.

2. An epoxy resin as in claim 1; wherein said aromatic hydrocarbon isselected from the class consisting of xylene, naphthalene and toluene.

3. An epoxy resin as in claim 2; wherein said oxygen containingcondensation product is the condensate of xylene and formaldehyde havinga molecular weight of at least 300.

4. An epoxy resin as in claim 3; wherein said reaction product is theproduct of reacting from 0.4 to 3 parts, by weight, of phenol with 1part of said condensation of xylene and formaldehyde.

5. An epoxy resin as in claim 1; wherein the reaction of the phenol withsaid oxygen containing condensation product is carried out in a mannerso as to introduce more than one phenolic hydroxy group per moleculeinto the condensation product forming the epoxy resin.

6. An epoxy resin as in claim 1; wherein the condensation ofepichlorohydrin with said reaction product is carried out in a manner soas to introduce more than one 4 epoxy group per molecule epoxy resin.

7. A resinous mixture capable of hardening at room temperature,consisting essentially of an amine containing at least two reactivehydrogen atoms; and an epoxy resin which is the condensation product ofepichlorohydrin and a substance which contains at least 2 aromaticnuclei per molecule and which is the reaction product of a mono-nuclearphenol and an oxygen containing condensation product of an aromatichydrocarbon and a compound selected from the class consisting offormaldehyde and paraformaldehyde, and which oxygen containingcondensation product is free of unreacted phenol, formaldehyde andparaformaldehyde.

8. A process for the production of cured resins comprising mixing anamine containing at least two reactive hydrogen atoms with a hardenableepoxy resin which is the condensation product of epichlorohydrin and asubstance which contains at least 2 aromatic nuclei per molecule andwhich is the reaction product of a mono-nuclear phenol and an oxygencontaining condensation product of an aromatic hydrocarbon and acompound selected from the class consisting of formaldehyde andparaformaldehyde, and which oxygen containing condensation product isfree of unreacted phenol, formaldehyde and paraformaldehyde.

9. A method of producing a hardenable epoxy resin consisting ofcondensing a member selected from the group consisting of formaldehydeand paraformaldehyde, with an aromatic hydrocarbon in the proportions of1 to 5 moles of said member per mole of said aromatic hydrocarbon, so asto produce a condensate with a molecular weight of at least 300 andwhich is free of unreacted quantities of said member; reacting 1 part byweight of said condensate with 0.4 to 3 parts of a mono-nuclear phenolso as to produce a novolak which contains at least 2 aromatic nuclei permolecule; and condensing epichloro hydrin with said novolak, in theproportions of 1 /2 to 5 moles of epichlorohydrin per phenolichydroxy-group in said novolak, in the presence of an alkaline catalystin the amount of 0.5 to 2 moles of the latter per phenolic hydroxy-groupin said novolak.

10. A method as in claim 9; wherein said catalyst is NaOH.

References Cited in the file of this patent UNITED STATES PATENTS

1. AN EPOXY RESIN WHICH IS THE CONDENSATION PRODUCT OF EPICHLOROHYDRINAND A SUBSTANCE WHICH CONTAINS AT LEAST 2 AROMATIC NUCLEI PER MOLECULEAND WHICH IS THE REACTION PRODUCT OF A MONO-NUCLEAR PHENOL AND AN OXYGENCONTAINING CONDENSATION PRODUCT OF AN AROMATIC HYDROCARBON AND ACOMPOUND SELECTED FROM THE CLASS CONSISTING OF FORMALDEHYDE ANDPARAFORMALDEHYDE, AND WHICH OXYGEN CONTAINING CONDENSATION PRODUCT ISFREE OF UNREACTED PHENOL, FORMALDEHYDE AND PARAFORMALDEHYDE.